In human hearing, hair cells in the cochlea respond to sound waves and produce corresponding auditory nerve impulses. These nerve impulses are then conducted to the brain and perceived as sound.
Damage to the hair cells results in loss of hearing because sound energy which is received by the cochlea is not transduced into auditory nerve impulses. This type of hearing loss is called sensorineural deafness. To overcome sensorineural deafness, cochlear implant systems, or cochlear prostheses, have been developed. These cochlear implant systems bypass the defective or missing hair cells located in the cochlea by presenting electrical stimulation directly to the ganglion cells in the cochlea. This electrical stimulation is supplied by an electrode array which is implanted in the cochlea. The ganglion cells then generate nerve impulses which are transmitted through the auditory nerve to the brain. This leads to the perception of sound in the brain and provides at least partial restoration of hearing function.
A cochlear prosthesis may typically comprise both an external unit that receives and processes ambient sound waves and an implant that receives data from the external unit and uses that data to directly stimulate the auditory nerve. Because the internal unit is surgically implanted, failure of the internal unit requires a surgical procedure to replace the damaged component. Failure of the internal unit may result from a variety of causes, such as damage from an impact.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.